On manual laterality (handedness) in humans and its forensic significance - a literature review.

Manual laterality (handedness) in humans has some significance for forensic practice where it is primarily employed in the form of handedness preference, based on a simplified three-stage classification (right-handed, left-handed and ambidextrous). In cases of homicide or suicide, the pattern of injuries, particularly cutting or stab injuries and gunshot wounds, may provide clues as to the perpetrator's handedness. In injuries inflicted by another person, the pattern of findings can in isolated cases allow to draw conclusions as to the handedness of the perpetrator. In self-inflicted injuries and suicide, the dominant hand is usually used either alone or as the lead hand. If it is found that fatal injuries were inflicted by the non-dominant hand, this gives rise to doubt that the manner of death is suicide. Evidence of handedness is of little value in distinguishing between suicide and homicide. Due to new developments in dentistry, imaging procedures and especially genetics, the utility of handedness in the identification of unknown persons or cadavers has significantly diminished. In living subjects, useful evidence of handedness can be obtained by observing the performance of specific gestures or activities. The subject should be asked to perform tasks involving one and two hands in a specific sequence. Standardised measurements of the morphology of the shoulders and upper extremities are able to make a statistical distinction between right and left. Since the accuracy of this process is, however, only,around 75 %, morphological determination of handedness should not be used in living subjects, but should be restricted to the identification of unknown cadavers or other post-mortem examinations.

Lateralisation abnormalities in obsessive-compulsive disorder: a line bisection study.

OBJECTIVE: Asymmetry in brain structure and function is implicated in the pathogenesis of psychiatric disorders. Although right hemisphere abnormality has been documented in obsessive-compulsive disorder (OCD), cerebral asymmetry is rarely examined. Therefore, in this study, we examined anomalous cerebral asymmetry in OCD patients using the line bisection task. METHODS: A total of 30 patients with OCD and 30 matched healthy controls were examined using a reliable and valid two-hand line bisection (LBS) task. The comparative profiles of LBS scores were analysed using analysis of covariance. RESULTS: Patients with OCD bisected significantly less number of lines to the left and had significant rightward deviation than controls, indicating right hemisphere dysfunction. The correlations observed in this study suggest that those with impaired laterality had more severe illness at baseline. CONCLUSIONS: The findings of this study indicate abnormal cerebral lateralisation and right hemisphere dysfunction in OCD patients.

Occupational ocular accidents amongst Greek endodontists: a national questionnaire survey.

AIM: To investigate amongst Greek endodontists, the incidence of ocular accidents during practice, the circumstances associated with them, the therapeutic measures taken after the accidents, their compliance with the use of eye protection and their eye care behaviour. METHODOLOGY: One hundred and forty-seven endodontists met the inclusion criteria and were invited to participate in the survey. Data were gathered through interviews based on a questionnaire. Participants were asked for personal/professional data, information on ocular accidents in the past 5 years, post-accident actions and the type of eye protection used. Their eyesight status and frequency of ocular examination were also recorded. Data were analysed using chi-square test, independent samples t-test and logistic regression. The level of significance was set at P = 0.05. RESULTS: The response rate was 84%. Ocular accidents were reported by 73% of the participants. Amalgam and NaOCl were the foreign bodies most frequently associated with ocular accidents. Medical assistance was sought in 16% of the most recent accidents. No permanent eye damage was reported. Regular use of magnification (OR:0.305, 95%CI:0.123-0.754) and years of clinical experience (OR:0.191, 95%CI:0.066-0.551) were significant predictors for the incidence of ocular accidents. Adequate eye protection was utilized by 82% of endodontists. Endodontists with eyesight deficiencies attended more frequently for ocular examination (P = 0.018). CONCLUSION: A high percentage of endodontists experienced ocular accidents. Regular use of magnification and increasing years in practice were associated with a reduced risk of ocular accidents. The majority of endodontists reported using adequate eye protection.

Lateral preference and schizotypy revisited: comparison of handedness measurement and classification methods.

A sample of 256 undergraduate students was administered five schizotypy scales and a lateral preference questionnaire consisting of 41 handedness items, in order to examine the effect of different approaches to the measurement and classification of handedness on the relationship between schizotypy and lateral preference. The extended handedness questionnaire included the 12 items of Annett's handedness questionnaire, the 10 items of Oldfield's (1971) Edinburgh Handedness Inventory, the 19 items of the lateral preference questionnaire used by Kelley and Coursey (1992a), and additional items from Steenhuis and Bryden's (1989) 32-item Waterloo Handedness Inventory, allowing the examination and comparison of a variety of handedness classification schemes and the computation of several continuous measures of handedness, and comparison of their relationships to schizotypy. Different approaches to the measurement and classification of handedness yielded somewhat different findings concerning the relationship to schizotypy, which also varied depending on gender and the schizotypy measure involved. Among males, higher schizotypy scores were associated with more dextral lateral preference, whereas among females higher schizotypy was associated with mixed right-handedness.

Hand dominance influences the processing of observed bodies.

In motor tasks, subgroups of lefthanders have been shown to differ in the distribution of attention about their own bodies. The present experiment examined whether similar attentional biases also apply when processing observed bodies. Sixteen right handers (RHs), 22 consistent left handers (CLHs) and 11 relatively ambidextrous inconsistent left handers (ILHs) performed an own body transformation task in which they were instructed to make speeded left-right judgements about a schematic human figure. Attentional biases associated with handedness were found to extend to observed bodies: CLHs' judgements were faster to the figure's left side, while ILHs, like RHs, showed facilitated performance to the figure's right side. These results demonstrate a novel embodiment effect whereby the processing of a static schematic human figure is modulated by an individual's personal motor capabilities. This finding suggests that motor simulation may contribute to whole body perception in the absence of actual or implied actions.

Degree versus direction: a comparison of four handedness classification schemes through the investigation of lateralised semantic priming.

Four classification systems were examined using lateralised semantic priming in order to investigate whether degree or direction of handedness better captures the pattern of lateralised semantic priming. A total of 85 participants completed a lateralised semantic priming task and three handedness questionnaires. The classification systems tested were: (1) the traditional right- vs left-handed (RHs vs LHs); (2) a four-factor model of strong and weak right- and left-handers (SRHs, WRHs, SLHs, WLHs); (3) strong- vs mixed-handed (SHs vs MHs); and (4) a three-factor model of consistent left- (CLHs), inconsistent left- (ILHs), and consistent right-handers (CRHs). Mixed-factorial ANOVAs demonstrated significant visual field (VF) by handedness interactions for all but the third model. Results show that LHs, SLHs, CLHs, and ILHs responded faster to LVF targets, whereas RHs, SRHs, and CRHs responded faster to RVF targets; no significant VF by handedness interaction was found between SHs and MHs. The three-factor model better captures handedness group divergence on lateralised semantic priming by incorporating the direction of handedness as well as the degree. These findings help explain some of the variance in language lateralisation, demonstrating that direction of handedness is as important as degree. The need for greater consideration of handedness subgroups in laterality research is highlighted.

The relation between lateralisation, early start of training, and amount of practice in musicians: a contribution to the problem of handedness classification.

This study investigates the influence of extensive bimanual training in professional musicians on the incidence of handedness in the most basic form of right-handedness (RH) and non-right-handedness (NRH), according to Annett's "right shift theory". The lateralisation coefficients (LCs) of a total sample of 128 bimanually performing music students were calculated for speed, regularity, and fatigue of tapping by using the speed tapping paradigm. Additionally, the accumulated amount of practice was recorded by means of retrospective interviews. The proportion of designated right-handers (dRH) and non-right-handers (dNRH) in hand performance was identified by binary logistic regression from LCs. A proportion of 30.8% designated NRH in the group of musicians was found, while in the control group of non-musicians (matched for age range) a proportion of 21.7% designated NRH was observed. Incidence of dNRH was higher in string players (35.6%) than in pianists (27.1%). As an effect of the extensive training of the left hand, tapping regularity increased and tapping fatigue decreased among those participants who evidenced an increased amount of accumulated practice time on the instrument. However, speed difference between hands (as indicated by LCs) remained uninfluenced by bimanual training. This finding is in contrast to those of Jancke, Schlaug, and Steinmetz (1997). Finally, our study provides a more reliable (statistical) classification as an external criterion for future genetic analyses of handedness.

Patterns of hand preference for pairs of actions and the classification of handedness.

Pairs of actions such as write x throw and throw x racquet were examined for items of the Annett hand preference questionnaire (AHPQ). Right (R) and left (L) responses were described for frequencies of RR, RL, LR, and LL pairings (write x throw etc.) in a large representative combined sample with the aim of discovering the distribution over the population as a whole. The frequencies of RL pairings varied significantly over the different item pairs but the frequencies of LR pairings were fairly constant. An important difference was found between primary actions (originally write, throw, racquet, match, toothbrush, hammer with the later addition of scissors for right-handers) and non-primary actions (needle and thread, broom, spade, dealing playing cards, and unscrewing the lid of a jar). For primary actions, there were similar numbers of right and left writers using the 'other' hand. For non-primary actions more right-handers used the left hand than for primary actions but more left-handers did not use the right hand. That is, different frequencies of response to primary versus non-primary actions were found for right-handers but not for left-handers. The pattern of findings was repeated for a corresponding analysis of left-handed throwing x AHPQ actions. The findings have implications for the classification of hand preferences and for analyses of the nature of hand skill.

Evaluation of subjective perceived rating for grip strength depending on handedness for various target force levels.

BACKGROUND: Measurement of hand exertion is very important to quantify the risk of Work-related Musculoskeletal Disorders (WMSDs) in manufacturing fields. Although a direct measurement is the most accurate way to quantify physical load, it is expensive and time consuming. To solve this limitation, a subjective self-report method has been proposed as a possible alternative. OBJECTIVE: The purpose of this study was to analyze the accuracy of subjective perception for grip force exertions associated with handedness (dominant and non-dominant hands). METHODS: A total of nine healthy adults participated in this study. All participants were asked to exert hand grip forces for randomly selected target force levels without any information about the actual target force levels. Then, participants were also asked to rate the subjective perception of their exertion level using % Maximum Voluntary Contraction (MVC) after each hand grip force exertion. RESULTS: The trend of subjective perception for various target force levels was different according to the handedness. In the case of the dominant hand, participants tend to rate less MVC levels (under-estimation) than the actual target force levels at lower than 50% MVC, whereas they tend to rate more MVC levels (over-estimation) than the actual target force levels at higher than 50% MVC, respectively. In case of non-dominant hand, generally participants showed over-estimate for all levels of MVCs in this study. CONCLUSIONS: According to the results of this study, subjective perception of exertion showed different patterns on the handedness (S-shape for dominant hand vs. over-estimation for non-dominant hand) for various target force levels. Therefore, it would be necessary to apply different criteria for each hand to evaluate subjective perception of hand grip exertion tasks.

The distribution of hand preference is discrete: a taxometric examination.

The dominant genetic models of human handedness (Annett, 1985; McManus, 1985a) have contrasting views on its nature. Whereas Annett's model proposes that handedness is distributed continuously (following the distribution of performance asymmetries of the hands), McManus's model proposes that handedness is distributed dichotomously. The aim of this study was to investigate the nature of the underlying distribution. The taxonomy of hand preference was analysed by two independent taxometric procedures, 'mean-above-mean-below-a-cut' and 'maximum-eigenvalue', separately in two geographically, demographically, and culturally distinct samples; one of Australian adults (N=787), and the other of Serbian high school students (N=1,224). The analyses revealed a latent categorical structure in both samples, with estimated mean base-rates of a right-handed taxon of 0.80 and 0.94 from the two analyses of the adult sample and of 0.79 and 0.93 from the two analyses of the high school sample. Subsequent analyses showed that the initial right-handed class could be subdivided into consistent and inconsistent right-handed subclasses in both samples. A supplementary analysis, including a measure of hand proficiency in a subset of the sample of Australian adults (N=596), also revealed a latent categorical structure, showing evidence for a categorical latent structure from a continuous measure of hand performance. We conclude that the distribution of hand preferences in humans is discrete and not continuous.

Axonal bias at a representational border in adult rat somatosensory cortex (S1).

The cortex is a highly organized structure and this organization is integral to cortical function. However, the circuitry underlying cortical organization is only partially understood, thus limiting our understanding of cortical function. Within the somatosensory cortex, organization is manifest as a map of the body surface. At the level of the cortical circuitry the horizontal connections of Layer 2/3 express a physiological bias that reflects discontinuities within the somatosensory map. Both excitation and inhibition are smaller when evoked from across a representational border, as compared to when they are evoked from within the representation. This physiological bias may be due to a bias in either the strength or number of synapses and/or the number of axons that cross this border and the extent of their arborization. In this study we used both an anterograde (Phaseolus vulgaris leucoagglutinin) and a retrograde (cholera toxin B) tracer to examine Layer 2/3 horizontal projections in rat S1. We determined that there is a bias in the amount of horizontal axonal projections that cross the forepaw/lower jaw border as compared to projections remaining within an individual representation. This bias in axonal projection and the correlated bias in excitation and inhibition may underlie the expression of the representational border.

The influence of right frontotemporal dysfunction on social behavior in frontotemporal dementia.

BACKGROUND: Frontotemporal dementia (FTD) is associated with a variety of cognitive and behavioral dysfunctions. Symptoms may be influenced by the relative involvement of the right versus the left hemisphere, with left-sided FTD manifesting language changes and right-sided FTD presenting with aggressive, antisocial, and other socially undesirable behaviors. OBJECTIVE: To test the hypothesis that right-sided FTD is associated with socially undesirable behavior. METHODS: The authors assessed 41 patients with FTD diagnosed by the new research criteria for FTD(1) including behavioral, neuropsychologic, and neurologic testing as well as SPECT and MRI. Based on visual inspection of SPECT scans, 12 patients were classified as having predominantly right-sided and 19 patients were classified as having predominantly left-sided FTD. A clinician blinded to the imaging data reviewed medical records to tabulate the frequency of the following socially undesirable behaviors: criminal behavior, aggression, loss of job, alienation from family/friends, financial recklessness, sexually deviant behavior, and abnormal response to spousal crisis. RESULTS: Eleven of 12 right-sided and 2 of 19 left-sided FTD patients had socially undesirable behavior as an early presenting symptom (chi = 23.3, p < 0.001). CONCLUSION: The authors conclude that right-sided frontotemporal degeneration is associated with socially undesirable behavior. The early presence of socially undesirable behavior in FTD differentiates right-sided from left-sided degeneration. The results highlight the importance of the right hemisphere, especially frontotemporal regions, in the mediation of social behavior. The potential mechanism for these social losses with right-sided disease is discussed.

Cluster analysis reveals at least three, and possibly five distinct handedness groups.

Multivariate techniques have used data from hand preference questionnaires to group hand preference items, but no attempt has been made to date to use multivariate analyses to group individuals in terms of handedness groups. This study analyzed the responses of 645 subjects on the Waterloo 60-item handedness questionnaire with a cluster analysis (BMDP) in order to determine the grouping of individuals in terms of hand preference patterns. Five distinct handedness groups were recognized by this procedure and a Discriminant Function Analysis revealed a very high accuracy of assigning individuals to the five groups. A cluster analysis of a shorter 14-item questionnaire suggested three distinct handedness groups, and the degree of accuracy of assigning individuals to these groups was also very high. As is the case with all multivariate techniques in neuropsychology, the question of whether the clusters form meaningful groupings awaits an answer in terms of their different neuropsychological properties.

On the futility of using familial sinistrality to subclassify handedness groups.

Annett's right shift model was used to show that presence of left-handedness in parents or grandparents is an extremely weak indicator of whether or not a person's handedness is influenced by genetic factors. Furthermore, where a genetic influence is present, familial sinistrality is only weakly related to underlying genotype. The usual rationale given for subdividing handedness groups according to familial sinistrality is logically indefensible.

Motion analysis.

BACKGROUND: The ability to make an objective evaluation of a surgeon's operative ability remains an elusive goal. In this study, we used motion analysis as a measure of dexterity in the performance of a simulated operation. METHODS: Fifteen surgeons performed a total of 45 laboratory-based laparoscopic cholecystectomies on a cadaveric porcine liver model. Subjects were assigned to one of three groups according to their level of experience in human laparoscopic cholecystectomy. Electromagnetic tracking devices were used to analyze the surgeon's hand movements as they performed the procedure. Movement data (time, distance, number of movements, and speed of movement) were then compared. RESULTS: Analysis of variance (ANOVA) movement scores across the three groups showed significantly better performance among the experienced laparoscopic surgeons than the novices. Learning curves across repetitions of procedures were plotted. Novices made more improvement than experts. CONCLUSIONS: Motion analysis provides useful data for the assessment of laparoscopic dexterity, and the porcine liver model is a valid simulation of the real procedure.

Prevalence and handedness correlates of recurrent aphthous stomatitis in the Turkish population.

OBJECTIVES: The present study was designed to determine the relationship between recurrent aphthous stomatitis (RAS) and handedness, and to assess the prevalence of RAS in the Turkish population. METHODS: The present study was conducted among 11,360 persons (5,705 males and 5,655 females) with a mean age of 30.4 years. A questionnaire focusing on handedness was administered to these patients. Handedness was assessed according to the Edinburgh Handedness Inventory. The diagnosis of RAS was made on the basis of clinical appearance, location, and the patient's health history. RAS information of patients was collected by means of a data form specifically designed for this study. Subjects were informed about RAS. We took anamneses and filled out the investigation forms. Apart from patients with registration of current aphthae (average point prevalence, APP), patients who had a past two-year history (self-reported two-year prevalence, SRTP) of the lesion were also included in this study. Data were analyzed using the chi-square and logistic regression tests. RESULTS: The prevalence of RAS (APP) was 2.7 percent and that of a history of RAS (SRTP) 22.8 percent. Thus, the total prevalence (APP+SRTP), including present lesions and a two-year history (SRTP), was 25.5 percent. Adjusted results showed that females, left-handers, 10-30-year-olds, and nonsmokers were 1.53, 1.69, 2.05, and 1.61 times more likely to have RAS (APP+SRTP) than males, right-handers, 31-50-year-olds, and smokers, respectively (P<.0001). CONCLUSION: The present study suggests that left-handedness appears to be a predictor factor for RAS.

Inventory-derived task handedness preferences of nine professions and their associations with self-report global handedness preferences.

The handedness preference (laterality) of 1,196 professionals grouped in nine professions previously reported using self-reported global handedness and scores on a modified Edinburgh Handedness Inventory was further defined by evaluating the association between profession and the 10 manual tasks of the inventory. The previously reported ranking of professions in order of increasing righthandedness of laterality score arose from the handedness of specific inventory tasks. A similar association was found for self-reported global handedness. The evidence continues to support the hypothesis of an association between handedness preference and specific aptitudes or skills in this sample of professional persons.

Hand preference as related to development and behavior in infancy.

55 healthy infants were assessed for their developmental and behavioral patterns at the age of 9 mo. Hand preference was assessed at 20 mo. of age. The distribution of hand preference showed 12 were right-handed, 11 left-handed and 23 ambidextrous. This distribution appears shifted more to the left than that reported for older children. Although their data were based on different tests not appropriate for 9-mo.-old infants, ambidexterity appeared to reflect part of the hand-preference continuum. No significant relationship between hand preference and developmental attainments was noted. Perhaps a larger sample would provide a clear developmental behavioral pattern and hand preference in infancy.

Type II errors in comparisons of dextral and sinistral groups.

Anomalous cerebral dominance can have multiple manifestations, e.g., left-eye preference or left-foot preference in the absence of left handedness per se. The 1987 estimate of prevalence of anomalous dominance in the population by Geschwind and Behan approaches 30%, three times the estimate obtained by using handedness alone as the sorting criterion. Accordingly, substantial numbers of subjects assigned to "dextral" groups may actually display other legitimate indicators of anomalous dominance. As such there is a tendency to commit Type II errors in studies in which handedness alone is used to represent the variance attributed to cerebral dominance. Accordingly, null hypotheses assessing the relations of cerebral dominance with dependent variables are accepted even though they may, in fact, be false.

Consistency of hand use and sleep problems.

In this study, we measured the relationship between the consistency of hand use and three symptoms of insomnia, i.e., delayed sleep onset, frequent awakenings during sleep, and trouble returning to sleep after an awakening. For each of these insomnia-related symptoms, university students who were classified as inconsistent in the use of their hands (n = 30) were significantly more likely to report problems than their consistent hand-use peers (n = 30). These data were discussed both in relation to the literature on handedness classification and sleep problems and the emerging literature on consistency of hand use and health-related problems.